More low cost amplifier info. (I don't want to say hearing aid.)

They missed one *very* important requirement: immunity to pulsed radio signals, e.g. DECT, GSM etc.

I caused one hell of a stink at work and a major problem for my boss in the early 90s, when I demonstrated how extreme the problem could be.

Current hearing aids are pretty immune; many pieces of audio equipment aren't. You can often hear the de-de-de---de-de-de---de-de-de as a phone communicates with a basestation.

ome chatter. I thought I would post a link to this app note. I'm certain I have over-simplified the task as Tom pointed out. I am curious(like any ot her engineer) so I will see how far I can get in my workshop.

I was thinking NFMI would be the perfect technology for this application, b ut they beat me to it.

Such curiosity is a good thing.

Not understanding the field, and so taking a lot of time/effort to make /old/ mistakes /again/, is a waste of everybody's time.

Doubly so when the mistakes have already been solved :)

Points of information, that might hint at the complexity of the subject and non-obvious costs...

I haven't had a hearing assessment for >3 years and my aids are >3 years old, so the NHS has offered me more.

Taking moulds for both ears required 0.5 hours in a dedicated room with specialised equipment. It included a preliminary hearing assessment to ensure the moulds would be appropriate and that the appropriate type of aid would be available.

When the moulds have been made, the next appointment will take 1.5 hours. It will include - a detailed hearing test, - setting up the aids with several profiles so that I can use them in different circumstances, e.g. in a room, with winds, music, noise reduction - calibrating the operation of the aid in my specific ear. That's effectively adding a filter to cancel out my canal's time domain response

I will probably want to tweak the settings after I've tried them for a bit; that would be another

The costs of 2-3 hours consultations add up and are, of course, on top of the cost of the aid itself.

You missed out that all the NHS hearing tests are done in an acoustically isolated room which is quite an expensive to construction. They are typically a large bank of 1/3 octave bandpass filters to equalise the frequency response followed by a class D amplifier.

Really fancy ones will rescale frequency domain so that the parts needed for understanding speech are mapped onto the range of frequencies where you retain the most sensitivity. This utterly destroys music but makes speech a lot more intelligible for some people when they get used to it.

Yes, this was interesting to me. "Frequency shifting uses digital signal processing to shift speech to a lower frequency, which is helpful for people with high-frequency hearing loss."

I listen to a lot of old radio programs (40s and 50s) and there are times when there is a female voice that I cannot understand. On other recordings I understand the female voice just fine. I believe some of the problem is me and some is in the restoration of the recordings and how they processing the audio. Interesting article.

Yup, tis important.

I've mentioned that in other posts, and for brevity considered that part of "dedicated room" :)

In this case the room is in the basement centre of the building, and is partially covered with something acoustically absorbtive.

I've no idea how those would sound, but I bet it would be very strange for a while. Maybe I'll find out.

I'm sure it is me :(

Without my aids, I have that problem with current radio programmes. With the aids the problem is reduced but not eliminated.

I find lipreading radio newsreaders to be unsatisfactory at best ;}